T3D camera lenses as viewer lenses

[Peter Abrahams <telscope@xxxxxxxxxx>]

>>>>

The problem is that many lenses have the 

pupils buried in the glass.

Peter Abrahams should comment, but the problem with the pupils

being buried in the glass is that unless they are enormous, 

you won't get much field of view.  

<<<<<<<<

A Galilean ocular (a bi-concave lens) also 'buries' the exit pupil (in
this case making it virtual), they work but give a very small apparent
field of view.  At anything above 2 or 3 power, it's like looking down a
tube.


I was refraining because I didn't have anything constructive to say.  You
can use all kinds of things as eyepieces, a glass marble or a water drop
in a wire loop, a magnifying glass, or a camera lens.  I have a short
file of posts from people who have experimented with using camera lenses
on telescopes (different than a viewer).  A Canon 55mm f/1.2 gives a very
flat image, with pinpoint stars edge to edge, but only over a 40 degree
apparent field, which isn't ridiculous but isn't worth pursuing.   There
are also problems with huge exit pupils, the exiting beam is usually
quite a bit larger than your eye's pupil, so that light is wasted. 
Finally, the physical dimensions of most camera lenses preclude placing
two of them side by side for a binocular viewer.

If you've got a pile of camera lenses & need a viewer, try them out
before you buy some expensive viewer optics.  But the general- rule-
with- exceptions is that optical devices (except the very simplest) are
highly engineered to do a particular task & are not 'swappable', unless
you are oblivious to aberrations and limited field.   Of course, they're
also highly expensive, and so everyone is a hacker at some point.

_______________________________________

Peter Abrahams   telscope@xxxxxxxxxx

the history of the telescope, the microscope,

    and the prism binocular



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